1. Field of the Invention
The present invention relates, in general, to concentrators for use in the solar power industry, and, more particularly, to systems, devices and methods for more effectively concentrating solar energy (or, more simply, for concentrating sunlight) using an improved tracking concentrator such as a fiber optic wafer concentrator adapted for effective tracking of the Sun.
2. Relevant Background
In general, concentrated solar power systems use lenses or mirrors to focus a large area of sunlight onto a small area. Electrical power is produced when the concentrated light is directed onto photovoltaic surfaces or when the concentrated light is used to heat a transfer fluid for a conventional power plant (e.g., to run a turbine with steam).
With regard to the latter example, thermal concentrators have been around for many years, with concentrated solar thermal (CST) being used to produce renewable heat or electricity (which may be labeled thermoelectricity as it is usually generated via steam generation). A wide range of concentrating technologies exists with a parabolic trough being a popular choice for use in many CST systems. A parabolic trough includes a linear parabolic reflector that concentrates light onto a receiver that is positioned along the reflector's focal line. The receiver is typically a pipe or tube (i.e., is an absorber tube) positioned directly above the middle of the parabolic reflector (or mirrored surface that may be a coating of silver, polished aluminum, or the like). The pipe or tube is filled with a working or transfer fluid. The reflector is operated to attempt to accurately track the Sun's movements during daylight hours by tracking along a single axis. In some cases, the working fluid is an oil, a molten salt, or other material that is heated to high temperatures (300 to 700° F.) as it flows through the receiver, and fluid is then used as a heat source for a power generation system (e.g., to heat water to create steam that is used to turn a turbine generator or the like).
There is a strong desire to expand the use of renewable energy sources such as thermal concentrators. As discussed above, CST systems generally track the Sun east to west from the morning to evening hours, and this is done with a complex tracking system that tilts a linear parabolic concentrator or reflector, which may be may several hundred meters long and up to as much as ten or meters across. Generally, the lines or solar filed piping/absorber tubing of these systems are linked together to heat water and in turn generate steam to drive a turbine generator to provide electricity. The parabolic concentrators are generally made of glass with a mirror backing material and include a sturdy framing system that is positioned or controlled with a computerized one axis tracking system. The parabolic concentrators are generally focused to heat an absorber tube made of tempered glass and containing water, oil, or the like that is pumped through the tube (which is generally 5 to 10-inches in diameter) at the correct rate depending upon the length of the concentrator and corresponding to the overall size of the system.
While being desirable for using a renewable power source, CST systems, such as those that utilize parabolic concentrators with single-axis tracking capabilities, have not been widely adopted. One drawback with CST systems is that they tend to be quite inefficient, and this lack of efficiency is especially acute during months where the incidence angle of the sun is the furthest from perpendicular. Collecting efficiencies due to the skewed focus of the troughs can drop to under fifty percent in these conditions. In addition, the absorber tube or pipe carrying the heated fluid may be relatively large in diameter and is located directly in front of the concentrator (i.e., in the trough of the parabolic reflector or the like), which shadows the overall collection device and decreases efficiency further. Efficiencies of CST systems are a concern as the overall efficiencies from collector to grid may be as low as about fifteen percent. Hence, there is a need to enhance efficiencies at each step of the process including collection and thermal efficiencies proximate or within the collector assembly.
Additional drawbacks of conventional parabolic concentrators include expense of manufacturing, lack of efficiency during many months of the year (e.g., due to non ideal azimuth angles), and fragility of the parabolic trough materials (e.g., which may lead to damage under normal operating conditions such as due to weather conditions including hail, strong winds, and the like). In addition, parabolic reflectors or concentrators tend to be quite dangerous to work around during sunlight hours as they produce concentrated beams of sunlight that can cause severe burns and even blindness and as many of the parts of the system are at very high operating temperatures.
Further, one of the larger drawbacks is the need to maintain the reflector and absorber tubing outer surfaces in a very clean state to maintain light collection and thermal efficiencies in desired ranges. As a result, a problem with parabolic concentrators is the difficulty of cleaning the systems including the large usage of cleaning chemicals and water. Large systems require constant cleaning and rinsing, adding costs and, over time, contaminating soil underneath the reflectors. In desert conditions where many CST systems are located, it is particularly expensive and difficult to provide water for cleaning these units. Most arrays are cleaned by crews on an ongoing basis or seven days a week, which increases the maintenance or operating costs associated with generation of electricity with CST systems.
Hence, there remains a need for a more modern, scalable concentrator system. Preferably, such a concentrator system would be easier to clean including using less water and chemicals. The system may be cheaper to manufacture and less dangerous to operate and maintain (and more durable such as being less likely to be damaged by hail or the like). Further, the concentrator system may be more efficient (with a lower cost per watt of generated electricity). Still further, the concentrator system may be useful for heating a variety of transfer or working fluids including heating oil, glycol, air, or other liquids and also have the ability to function as a photovoltaic concentrator at the same time or independently from heating a working or transfer fluid.